The Israeli military describes the operation as open-ended, saying the objective is to strike a "significant blow to Hamas' terror infrastructure."

Israeli Prime Minister Benjamin Netanyahu's office says he instructed the army to go ahead after Hamas rejected an Egyptian cease-fire plan earlier in the week and after Israeli forces stopped Hamas militants as they tried to infiltrate into Israel through a tunnel from Gaza earlier today. The statement says Israel "is obliged to protect its citizens" from what it describes as "relentless aggression by Hamas."

Hamas officials had no immediate comment.

It's the first major Israeli ground offensive in Gaza in just over five years.

The operation followed a brief truce earlier today in which Israel held fire to allow Gazans to stock up on food and other necessities after being largely holed up at home since the conflict began last month.

Raw Video: Israeli Ground Offensive in Gaza StripAssociated Press

Raw Video: Israeli Ground Offensive in Gaza Strip (Associated Press) Israeli forces on Thursday launched a ground offensive in the Gaza Strip, the military said. The operation came after 10 days of intense fighting between Israel and the Islamic militant group, Hamas. (July 17)